Chemical erasing of photographic silver images



Patented Jan. I 7, 1950 CHEMICAL ERASING OF PHOTOGRAPHIC SILVER IMAGESJohn F. Kienast, River Edge, N; J assignor to Keufiel & Esser Comcorporation of New J c pany, Hoboken, N. J,, a rsey No Drawing.Application November 10, 1944, 'fSerial No. 562,916

This invention relates to a method for and compositions useful in themaking of erasures on photographic prints.

In engineering reproduction materials and particularly those whichemploy silver to produce the visible image, it is oftentimes desirableto make erasures by removing the silver which colors some of the areas,either to correct errors or to remove lines from certain portions inorder that they may be corrected or redrawn.

The invention is applicable to many types of photographic materials onvarious base stocks such as paper, cloth, film, sheet metal, etc.,including: those commonly referred to as vandykes, brown prints and thelike where the image is created from a combined soluble silver salt andan iron salt; engineering reproduction materials with silver halideemulsions; engineering reproduction materials having gum or gluebichromate with silver images and the like; and may also be used forcorrecting ordinary photographic film as well asphotographic printswhich latter are oftentimes referred to as photoprints or photocopies.

In the past, various procedures have been proposed for making thecorrections in a silver image and one of the early methods included theapplication of a single fluid eradicator, the principal constituent ofwhich was mercuric chloride. Erasures made with this material werefugitive and became opaque when exposed to light, corroded pens anddrawing instruments which were later used on the areas, had some dangerfrom toxicity and produced "ghosts which showed up when the photographicmaterial was used for reproduction purposes.

Some improvement in erasing fluids occurred by applying hypochlorite inthe form of sodium hypochlorite which was the first step in removing theimage. For the second step the area was treated with a hypo fixingsolution. Results were not generally satisfactory or uniform because itwas difficult to stabilize the hypochlorlte which deteriorated instorage or, if stabilized with alkali, had a deleterious effect on thebase material when applied to make an erasure. It was diflicult to makea drawing over an erased area particularly when ink lines were employed,as

the ink spread through the base which was oftenso weakened that it wouldcrack or disintegrate.

It has now been discovered that the undesirableeffects and disadvantagesof prior art methods can be avoided by using two solutions successivelyin the manner hereinafter described, when it i '1 Claims. (01. 95-43)desired to make erasures of images which were created'photographicallyfrom silver salts.

In order to carry out this invention; a eupric halide, preferably cupricchloride, is dissolved in water in quantities ranging from 3% to withbest results obtained from cupric chloride representing approximately15%. This material is stable in storage, the desired concentration isreadily secured and it does not in any manner attack the base sheet.

Improved results are obtained by the addition of an ammonium halidewhich may correspond with the cupric salt. Where thisis ammoniumchloride, it is used in amounts ranging from a concentration of 5% to ashigh as 25% with amounts approximately 15% being satisfactory for mostpurposes. The solubility of the ammonium chloride is determined bytheamount of the cupric chloride already in solution, that is, thegreater the concentration of cupric chloride theless ammonium chloridewill go into solution. It is preferable to use the maximum quantity thatcan be dissolvedin the cupric chloride solution already prepared. Theammonium chloride improves the action of the first fluid by increasingthe speed of makes possible a fluid is applied, which is somewhatcleaner, i. e. more complete, than if the cupric chloride is used alonein the first solution.

A preferred solution portions-z Distilled water, 1000 cc. Cupricchloride (CuClz.2HzO), 167 gms.

The second solution used for making erasures is an aqueous solution ofthiourea. Preferably,

this solution also contains a suitable wetting agent of the types hereinset forth. In the preferred composition the thiourea is dissolved inwater to make a saturated solution. About one and one-quarter (1% lbs.)poundswill dissolvein one gallon of water at normal room tempera-1 Sucha solution with small amounts of a wetting agentis stable underconditions of.

tures.

normal storage and use. To either theerasing fluid or the fixing fluidor both, a wetting agent such as alcohol, sulphonated alcohol, di hexylsodium sulfosuccinate.

or the like may be added in small amounts. l In order to make anerasure, the cupric chloride solution, with or without ammonium chlorideand.

a wettingagent. is applied to the area where the the first reaction andit also final erasure after the second' has the following pro-.-

blotted from: the surface promptly after ithas been applied uniformlyover the area to be treated. After the excess liquid has been removed byblotting, the second solution of thiourea and the wetting agent isapplied to the same area though for many types of engineeringreproductionsit need not be so limited. The solution may be permitted todry on the sheet but: it is usually; preferred to remove blotting. Itcan, of course, be

avoided.

The combination of the cupric chloride solution and the thioureasolution for erasing has many advantages over other erasing fluids. Aprior two-fluid combination for erasing which included a first solutioncomprising cupric chloride presented diifi'culties in use because it wasnecessary to insure thorough conversion of the image withthe cupricchloridebefore its blotting and the application of a fixing solution,otherwise the erasure will not be complete and even if the process iscarried out carefully it is possible that there may be some staining ofthe print, a condition which is particularly undesirable whereengineering reproductions are concerned. This was likely to occur inthose cases where the print had been prepared-under conditions wherespecial treatments had been given either" to accelerate the originalreproduction process or where final washingwas inadequate or incomplete.Under such cases residual salts left in the base material adverselyaffected theerasing action and in some instances resulted inproducing'colored compounds that left an apparently permanent stain inthe drawing.

Where the present composition is used, i. e. the thiourea solution isapplied to the print'aft'ei' treatment with the cupric chloridesolution, the critical procedural details formerly necessary can bedispensed with. Excellent erasures are secured evenwhere residual saltsfrom the original" development have not been adequately or completelyremoved. The erasure restores the original color of the base sheet.

Instead of using cupric chloride for the first solution, other oxidizingor decolorizing solutions may be employed. Another. is ammonium orpotassium persulfate saturated solution which, however, has nodiscernable efiect when first applied but produces the erasure when thesolution of thiourea is also present; These two solutions cannot bepremixed though both must'be present simultaneously.

The compositions herein described, when used in the process as setforth, will remove silver images from paper, cloth, film, metal or otherbases normally used as supports for light sensitive layers containingsilver and will produce erasures which are very permanent and do notaffect the base either as to strength or" as to ability to receiveredrawn lines. The erasure does" not leave any residue which appears onthe'print when the. erased sheet is used in making reproductions as, forexample, by contact printing.

The cupric chloriderequired in the firstfluid may be obtained not'onlyby dissolving the'salt' cupric chloride in waterbut also by providingthe residual liquid as by washed from the surface in any known mannerbut this results. in unduly Wetting the sheet and is preferably 1 Cupricfluoride works slowly upon and from 25' to in solution the divalentcupric ion from any other source such as copper sulfate and the chlorideion from any suitable chloride salt as, for example, sodium chloridethereby providing in the solution the divalent cupric ion and thechloride ion. :The ammonium chloride desired inthe solution may also beprovided by theionization of ammonium salts and chloride salts.

Other cupric halides in addition to the cupric chloride discussed abovemay be used although results are generally not as efiective. Forexample, cupric bromide works very slowly and the addition. of ammoniumbromide has no noticeable effect. Onthe other hand, the addition ofammonium'chloride greatly improves the action. the addition of. ammoniumfluoride and, of course, more rapidly if ammonium chloride is added.

It should be understood that where reference is made to a solution ofcupric halide, this expression is intended to'mean that the solutioncontains cuprlc'ions and halide ions even though not obtained directlyby the solution" of the cupric halide;

While the invention. has been described with reference to certainpreferred procedures and compositions, theseareto be considered asillustrative of the invention as defined in the appended claims.

Iclaim:'

l. The process for erasing silver images on bases which comprisesapplying to that portion of the image'which is to be erased a solutioncontaining between 3 and 58% of cupric chloride 5%. of ammoniumchloride, treating the areato which the cupric chloride solution wasapplied-with a substantially saturated solution of thiourea-and removingthe resulting solution.

2. The process for erasing silver. images on baseswhichcomprises'applying to that portion ofv the image which is. to be eraseda solution containing cupric chloride and 15% ammo-- nium chloride,treating the area to which-the cupric chloride solution was applied-witha substantially saturatedsolution of-thiourea and removing theresultingsolutionn 3. Aucompositionior making erasures oi silver imageswhich comprises anaqueous solution consisting essentially of- 3 to 50%cupric chlo-. ride andammonium chloride ina sufficient concentration ofiron 1.25 to 5% to form a substantially saturated solution in water.

i. A composition for making erasures of'sil-.. ver images whichcomprises an aqueous solu,

tion consisting essentially of a, wetting agent,

from 3 to 58% cupric chloride and ammonium chloride in'a suiiicientconcentration of from to 5% to form a substantially saturated solutionin water. I g 7 5. A composition for making erasures of silver images byapplyingthecomposition to-that portion of theimage which is to beerasedand thereafter treatingthe area' towhi'ch the com position has beenapplied with a substantially saturated solution of 'thicurea, saideomp'os ionconsisting essentially of 1 approximately 15% cupric chlorideammonium chloride in a suilicient concentration of approximately15%"to 2form a substantiallysaturated solution in water 6. The process forerasing silver images on bases which comprises applyingto-that portionof the-image which is to be erased asolution" containing'betweens andofcupric chleride, treating the area "to which the cupric. chlo-REFERENCES CITED The following references are of record in the file ofthis patent:

Number Name Date 1,780,025 Mankenberg Oct. 28, 1930 1,945,658 RoesslerFeb. 6, 1934 5 1,963,197 Frohlich June 19, 1934 2,000,353 Schaeffer May7, 1935 2,100,594 Heymer Nov. 30, 1937 2,107,094 Townsend Feb. 1, 19382,166,617 Weber et a1. July 18, 1939 10 2,311,015 Young et a1 Feb. 16,1943 2,322,084 Young et al June 15, 1943 2,327,822 Russell et a1 Aug.24, 1943 OTHER REFERENCES 15 Clerc: Photography Theory and Practice,

6 U'NI'I'ED STATES PATENTS Pitman 8: Sons, New York, 1937, p. 270 cited.

1. THE PROCESS OF ERASING SILVER IMAGES ON BASES WHICH COMPRISESAPPLYING TO THAT PORTION OF THE IMAGE WHICH IS TO BE ERASED A SOLUTIONCONTAINING BETWEEN 3 AND 50% OF CUPRIC CHLORIDE AND FROM 25 TO 5% OFAMMONIUM CHLORIDE, TREATING THE AREA TO WHICH THE CUPRIC CHLORIDESOLUTION WAS APPLIED WITH A SUBSTANTIALLY SATURATED SOLUTION OFTHIROUREA AND REMOVING THE RESULTING SOLUTION.